Electric Heat Defrost Alogrithm

ABSTRACT

A method of operating an HVAC system is provided. The method comprises, when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, continuing to operate a supplemental heat generator that was in operation in the defrost mode. The method further comprises, after a period of time in the defrost recovery mode has passed, deactivating at least a first portion of the total heating capacity of the supplemental heat generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/943,828 filed on Feb. 24, 2014 by Leslie Lynn Zinger and entitled “Electric Heat Defrost Algorithm,” the disclosure of which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Heating, ventilation, and/or air conditioning systems (HVAC systems) may be used to heat and/or cool comfort zones to comfortable temperatures. Comfort zones are often the occupiable portions of residential and/or commercial areas and may be subject to variable zone conditions, such as temperature and humidity. A portion of an HVAC system may be installed outdoors or in some other location remote from the comfort zone for the purpose of performing heat exchange. Such a location may be referred to as an ambient zone and may also have variable temperature and humidity conditions.

Some HVAC systems are heat pump systems. Heat pump systems are generally capable of operating in a cooling mode in which a comfort zone is cooled by transferring heat from the comfort zone to an ambient zone using a refrigeration cycle (e.g., the Rankine cycle). Heat pump systems are also generally capable of operating in a heating mode in which the direction of refrigerant flow through the components of the HVAC system is reversed so that heat is transferred from the ambient zone to the comfort zone, thereby heating the comfort zone. Heat pump systems generally use a reversing valve for rerouting the direction of refrigerant flow between the compressor and the heat exchangers associated with the comfort zone and the ambient zone.

If moisture is present in an ambient zone, the moisture may condense on the ambient zone components of an HVAC system. Accordingly, when the temperature in the ambient zone is below a freezing point, frost and/or ice may accumulate on the outdoor portions of the HVAC system, sometimes necessitating a defrosting of the components of the HVAC system on which frost and/or ice have accumulated. In a heat pump system, the defrosting may be achieved by reversing the direction of refrigerant flow from the direction of flow used in the heating mode. Specifically, the refrigerant flow is such that heat is transferred from the comfort zone to the ambient zone during the defrosting of the HVAC system components.

SUMMARY

In an embodiment, a method for operating an HVAC system is provided. The method comprises, when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, continuing to operate a supplemental heat generator that was in operation in the defrost mode. The method further comprises, after a period of time in the defrost recovery mode has passed, deactivating at least a first portion of the total heating capacity of the supplemental heat generator.

In another embodiment, an HVAC system is provided. The HVAC system comprises a supplemental heat generator configured such that, when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, the supplemental heat generator continues operation that began in the defrost mode. The supplemental heat generator is further configured such that, after a period of time in the defrost recovery mode has passed, at least a first portion of the total heating capacity of the supplemental heat generator is deactivated.

In another embodiment, a method for operating an HVAC system is provided. The method comprises, when a supplemental heat generator in the HVAC system is activated in a defrost mode of the HVAC system, activating less than the total heating capacity of the supplemental heat generator. The method further comprises, when the defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, continuing to operate the supplemental heat generator.

The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments of the disclosure, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a simplified block diagram of an HVAC system according to an embodiment;

FIG. 2 is graph of discharge air temperature versus time during and after a defrost mode with no electric heat;

FIG. 3 is graph of discharge air temperature versus time during and after a defrost mode with electric heat;

FIG. 4 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to an embodiment of the disclosure;

FIG. 5 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to another embodiment of the disclosure;

FIG. 6 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to another embodiment of the disclosure;

FIG. 7 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to another embodiment of the disclosure;

FIG. 8 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to another embodiment of the disclosure;

FIG. 9 is graph of discharge air temperature versus time during and after a defrost mode with staged electric heat, according to another embodiment of the disclosure;

FIG. 10 is a flow chart of a method for operating an HVAC system according to an embodiment of the disclosure; and

FIG. 11 illustrates an exemplary general-purpose computer system suitable for implementing the several embodiments of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a simplified schematic diagram of a heating/ventilation/air conditioning system 100 (hereinafter referred to as an “HVAC system 100”) according to an embodiment. The HVAC system 100 operates to selectively control the temperature, humidity, and/or other air quality factors of a comfort zone 102. The HVAC system 100 generally comprises an ambient zone unit 104 and a comfort zone unit 106. The ambient zone unit 104 comprises a compressor 108, an ambient zone heat exchanger 110, and an ambient zone fan 112. The comfort zone unit 106 comprises a restriction device 114, a comfort zone heat exchanger 116, and a comfort zone blower 118. Refrigerant is carried between the compressor 108, the ambient zone heat exchanger 110, the restriction device 114, and the comfort zone exchanger 116 through refrigerant tubes 120.

The comfort zone blower 118 forces air from the comfort zone 102 into contact with the comfort zone heat exchanger 116 and subsequently back into the comfort zone 102 through air ducts 122. Similarly, the ambient zone fan 112 forces air from an ambient zone 124 into contact with the ambient zone heat exchanger 110 and subsequently back into the ambient zone 124 along an ambient air flow path 126. The HVAC system 100 is generally controlled by interactions between a controller 128 and a communicating thermostat 130. The controller 128 comprises a controller processor 132 and a controller memory 134, while the communicating thermostat 130 comprises a thermostat processor 136 and a thermostat memory 138.

Further, the controller 128 communicates with an ambient zone temperature sensor 140, while the communicating thermostat 130 communicates with a comfort zone temperature sensor 142. In this embodiment, communications between the controller 128 and the communicating thermostat 130, the controller 128 and the ambient zone temperature sensor 140, and the communicating thermostat 130 and the comfort zone temperature sensor 142 are bidirectional. Further, communications between the controller processor 132 and the controller memory 134 and between the thermostat processor 136 and the thermostat memory 138 are bidirectional. However, in alternative embodiments, the communication between some components may be unidirectional rather than bidirectional.

The HVAC system 100 is called a “split system” because the compressor 108, ambient zone heat exchanger 110, and ambient zone fan 112 are co-located in the ambient zone unit 104 while the restriction device 114, comfort zone heat exchanger 116, and comfort zone blower 118 are co-located in the comfort zone unit 106 separate from the ambient zone unit 104. However, in alternative embodiments of an HVAC system, substantially all of the components of the ambient zone unit 104 and the comfort zone unit 106 may be co-located in a single housing in a system called a “package system.” Further, in some embodiments, an HVAC system may include heat generators, such as electrically resistive heating elements and/or gas furnace elements, located in a comfort zone blower airflow path shared with a comfort zone heat exchanger.

While the comfort zone 102 may commonly be associated with a living space of a house or an area of a commercial building occupied by people, the comfort zone 102 may be also be associated with any other area in which it is desirable to control the temperature, humidity, and/or other air quality factors, such as computer equipment rooms, animal housings, or chemical storage facilities. Further, while the comfort zone unit 106 is shown as being located outside the comfort zone 102 (e.g., within an unoccupied attic or crawlspace), the comfort zone unit may alternatively be located within or partially within the comfort zone 102 (e.g., in an interior closet of a building).

Each of the ambient zone heat exchanger 110 and the comfort zone heat exchanger 116 may be constructed as air coils, shell and tube heat exchangers, plate heat exchangers, regenerative heat exchangers, adiabatic wheel heat exchangers, dynamic scraped surface heat exchangers, or any other suitable form of heat exchanger. The compressor 108 may be constructed as any suitable compressor, for example, a centrifugal compressor, a diagonal or mixed-flow compressor, an axial-flow compressor, a reciprocating compressor, a rotary screw compressor, a rotary vane compressor, a scroll compressor, or a diaphragm compressor. In some cases, the compressor 108 may be capable of operating in multiple stages (e.g., stage A and stage B). For example, the compressor 108 may be operated at a low speed (stage A) or a high speed (stage B). Alternative embodiments of an HVAC system may comprise one or more compressors that are operable at more than one speed or at a range of speeds (i.e., a variable speed compressor).

Further, while the HVAC system 100 is shown as operated in a cooling mode to remove heat from the comfort zone 102, the HVAC system 100 is configured as a “heat pump” system that selectively allows flow of refrigerant in the direction shown in FIG. 1 to cool the comfort zone 102 or in the reverse direction to that shown in FIG. 1 to heat the comfort zone 102 in a heating mode. It will further be appreciated that, in alternative embodiments, a second restriction device substantially similar to restriction device 114 may be incorporated into an ambient zone unit to assist with operation of an HVAC system in a heating mode substantially similar to the heating mode of HVAC system 100.

In the cooling mode, the compressor 108 operates to compress low pressure gas refrigerant into a hot and high pressure gas that is passed through the ambient zone heat exchanger 110. As the refrigerant is passed through the ambient zone heat exchanger 110, the ambient zone fan 112 operates to force air from the ambient zone 124 into contact with the ambient zone heat exchanger 110, thereby removing heat from the refrigerant and condensing the refrigerant into high pressure liquid form. The liquid refrigerant is then delivered to the restriction device 114. Forcing the refrigerant through the restriction device 114 causes the refrigerant to transform into a cold and low pressure gas. The cold gas is passed from the restriction device 114 into the comfort zone heat exchanger 116. While the cold gas is passed through the comfort zone heat exchanger 116, the comfort zone blower 118 operates to force air from the comfort zone 102 into contact with the comfort zone heat exchanger 116, heating the refrigerant and thereby providing a cooling and dehumidifying effect to the air, which is then returned to the comfort zone 102. In this embodiment, the HVAC system is using a vapor compression cycle, namely the Rankine cycle. In the heating mode, generally, the direction of the flow of the refrigerant is reversed compared to that shown in FIG. 1 so that heat is added to the comfort zone 102 using a reverse vapor compression cycle, namely the reverse Rankine cycle. It will be appreciated that alternative embodiments of an HVAC system may use any other suitable thermodynamic cycle for transferring heat to and/or from a comfort zone.

Generally, the controller 128 communicates with the ambient zone temperature sensor 140 that is located in the ambient zone 124 (e.g., outdoors, outdoors within the ambient zone unit in an embodiment where the ambient zone unit is located in the ambient zone, adjacent to the ambient zone unit in an embodiment where the ambient zone unit is located in the ambient zone, or any other suitable location for providing an ambient zone temperature or a temperature associated with the ambient zone). While the controller 128 is illustrated as positioned within the ambient zone unit 104, in alternative embodiments, the controller 128 may be positioned adjacent to but outside an ambient zone unit, outside a comfort zone, within a comfort zone unit, within a comfort zone, or at any other suitable location. It will be appreciated that, in alternative embodiments, an HVAC system may comprise a second controller substantially similar to controller 128 and that the second controller may be incorporated into a comfort zone unit substantially similar to comfort zone unit 106. In the embodiment shown in FIG. 1, through the use of the controller processor 132 and the controller memory 134, the controller 128 is configured to process instructions and/or algorithms that generally direct the operation of the HVAC system 100.

If the temperature in the ambient zone 124 is low, ice or frost may form on portions of the HVAC system 100 that are located in the ambient zone 124, such as the coils in the ambient zone heat exchanger 110. To prevent or mitigate the formation of ice or frost on the ambient zone portions of the HVAC system 100, the HVAC system 100 may enter a defrost mode. Entry into the defrost mode may be triggered when frost is detected on a portion of the ambient zone unit 104, or the defrost mode may be entered at regular intervals when ambient conditions are conducive for frost formation, or the defrost mode may be entered based on some other parameter.

In defrost mode, the HVAC system 100 heats the ambient zone portions of the system by entering the cooling mode. That is, refrigerant flow is directed such that heat is removed from the comfort zone 102 and is added to the portions of the ambient zone unit 104 that may be subject to frosting. If supplemental heat is not added to the air supplied to the comfort zone 102 while defrost mode is active, the supplied air may be uncomfortably cool at a time when comfort zone occupants are expecting warm air to be supplied. The term “discharge air” will be used herein to refer to the air that is provided to a comfort zone.

A situation where no supplemental heat is provided during defrost mode is illustrated in FIG. 2, where the temperature of the air provided to a comfort zone is plotted versus time. When defrost mode is entered at time 0, the discharge air has a temperature of approximately 95° F. In this and subsequent examples, the discharge air is assumed to have a temperature of approximately 95° F. during typical operation of heating mode, but it should be understood that air may be supplied at other temperatures during heating mode. As defrost mode progresses, the discharge air temperature drops steadily to approximately 43° F. at the time defrost mode ends approximately seven minutes later. At that time, the HVAC system returns to heating mode, and the discharge air temperature steadily climbs until returning to approximately 95° F. approximately 13 minutes after defrost mode began.

Such a large drop in discharge air temperature during defrost mode may cause discomfort among comfort zone occupants. Warmer discharge air may be provided during defrost mode by adding supplemental heat to the air supplied to the comfort zone. For example, an HVAC system may include supplemental heat generators such as electrically resistive heating elements and/or gas furnace heating elements located in the airflow path of the comfort zone blower. Any such supplemental heat generators may be referred to hereinafter as electric heaters or electric heat, but it should be understood that the supplemental heat generators may take other forms. When defrost mode is entered, the electric heaters may be activated in order to warm the air being supplied to the comfort zone.

The use of electric heat during defrost mode is illustrated in FIG. 3. The lower curve reproduces the case of no electric heat shown in FIG. 2, and the upper curve depicts discharge air temperature with supplemental electric heat. In this case, the full capacity of the electric heat is activated as defrost mode is entered. It can be seen that the addition of the electric heat results in a discharge air temperature of approximately 123° F. at that time. After approximately three minutes, the discharge air temperature drops to the approximately 95° F. level that existed before defrost mode was entered. The discharge air temperature continues to drop until reaching approximately 72° F. at the time defrost mode ends approximately seven minutes after beginning. At that time, the HVAC system returns to heating mode, the electric heat is deactivated, and the discharge air temperature drops to approximately 45° F. From that time onward, the discharge air temperature exhibits substantially the same behavior as in the case of FIG. 2 where no electric heat was provided.

It can thus be seen that the use of electric heat may prevent the drastic drop in discharge air temperature from approximately 95° F. to approximately 43° F. that may occur in defrost mode without electric heat. However, in the example of FIG. 3, during approximately the first three minutes of defrost mode, the discharge air temperature is greater than that typically provided in heating mode. Such a higher than normal discharge air temperature may not only be uncomfortable for the comfort zone occupants but may also waste energy.

In addition, the electric heat is typically completely shut off when defrost mode ends and heating mode resumes. The system had been in cooling mode during defrost mode, and the cooling coils may remain cold for some time as heating resumes. This can result in a period in the first few minutes after the end of defrost mode in which discharge air with a lower than desired temperature is provided to the comfort zone. Such a “cold blow” condition can be seen in FIG. 3, where the discharge air temperature is approximately 45° F. at the beginning of heating mode and does not return to the approximately 95° F. level until approximately six minutes later. Providing cool air in this manner during heating mode may cause discomfort among comfort zone occupants.

In an embodiment, electric heat is activated in stages near the beginning of defrost mode and deactivated in stages after defrost mode ends. Such staged activation and deactivation of electric heat may prevent air that is excessively warm from being provided to a comfort zone as the result of the activation of a defrost mode and may prevent air that is excessively cool from being provided to a comfort zone as the result of the deactivation of a defrost mode.

More specifically, when defrost mode is activated, electric heat may be brought on only in a first stage to offset the cooling provided by the cooling mode. This first stage may provide less heat than is provided by the entire electric heating system, thus preventing excessively warm air from being supplied to the comfort zone. As cooling of the discharge air continues during defrost mode, a second stage of electric heat may be brought on to provide additional heat and offset the additional cooling. Such activation of electric heat may continue in stages up to the number of heating stages available in the HVAC system. Alternatively, activation of electric heat may continue in stages until a desired discharge air temperature is reached. As used herein, the terms “stage” or “heating stage” may refer to a portion of the full capacity of a heating system, such as one bank of electric heating elements in a plurality of banks of electric heating elements or one set of gas furnace heating elements among a plurality of gas furnace heating elements.

The period of time from the time defrost mode ends to the time the discharge air temperature with no electric heat returns to its typical heating mode operating level may be referred to as defrost recovery. In an embodiment, when defrost mode ends and defrost recovery begins, electric heat may be turned off in stages rather than being completely shut off all at once. That is, at some period of time after defrost mode has ended and heating mode has resumed, one of the stages of electric heat that was turned on during defrost mode is turned off. As defrost recovery progresses, additional stages of electric heat may be turned off in succession until all of the stages are deactivated. In this way, uncomfortably cool air is not supplied during defrost recovery, and the temperature of the air provided to a comfort zone during defrost recovery may be kept near a desired level.

The upper curve of FIG. 4 illustrates discharge air temperatures that may be achieved when such a staged activation and deactivation of electric heat is implemented. It can be seen that electric heat is not activated immediately upon activation of defrost mode. Instead, a first stage of electric heat is activated approximately one minute after defrost mode is activated. The first stage of electric heat causes the discharge air temperature to rise from approximately 83° F. to approximately 90° F. Approximately 2.5 minutes after activation of defrost mode, a second stage of electric heat is activated, which causes the discharge air temperature to rise from approximately 80° F. to approximately 88° F. Approximately 3.5 minutes after activation of defrost mode, a third stage of electric heat is activated, which causes the discharge air temperature to rise from approximately 81° F. to approximately 89° F. In this example, the HVAC system has only three stages of electric heat, so all available electric heat has been activated after the third stage has been activated. In other embodiments, other numbers of stages of electric heat may be available. In addition, in other embodiments, the length of time until the first stage of electric heat is activated and the lengths of times between activations of subsequent stages may be different from the times shown.

The slight delay in the activation of electric heat and the activation of electric heat in stages may prevent excessively warm air from being supplied when defrost mode is entered. For example, in FIG. 3, where all available electric heat is activated upon activation of defrost mode, the discharge air temperature starts at approximately 123° F. when defrost mode begins and remains above 95° F. for approximately three minutes. Heating the discharge air to such high levels may waste energy, and such warm air may feel uncomfortable to comfort zone occupants. By contrast, in embodiments where electric heating is activated in stages during defrost mode, the discharge air temperature in defrost mode may not substantially exceed the levels typically maintained during heating mode, thus saving energy and improving occupant comfort. For example, in the embodiment depicted in FIG. 4, the discharge air temperature does not exceed approximately 95° F. during defrost mode.

It can also be seen from FIG. 4 that electric heat remains activated for a period of time after defrost mode ends and is deactivated in stages during defrost recovery. The discharge air temperature is approximately 72° F. approximately seven minutes after the beginning of defrost mode at the time when defrost mode ends and heating mode resumes. All stages of electric heat remain on at that time, and the discharge air temperature rises to approximately 103° F. approximately three minutes later. At that time, a first stage of electric heat is deactivated, and the discharge air temperature drops to approximately 96° F. A few moments later, a second stage of electric heat is deactivated, and the discharge air temperature drops to approximately 91° F. Approximately two minutes later, the third and last stage of electric heat is deactivated, and the discharge air temperature drops to approximately 90° F. From that time on, the discharge air temperature exhibits behavior substantially similar to the case where no electric heating occurs. In other embodiments, the length of time until the first stage of electric heat is deactivated and the lengths of times between deactivations of subsequent stages may be different from the times shown.

The continuation of electric heat in such a manner during defrost recovery may prevent the “cold blow” situation described above in which uncomfortably cool air is provided to a comfort zone for a period of time after the end of defrost mode. For example, in FIG. 3, when all electric heat is turned off at the end of defrost mode, the discharge air temperature drops almost immediately from approximately 72° F. to an uncomfortably low level of approximately 45° F. The discharge air temperature does not reach the approximately 95° F. level typically maintained during heating mode until approximately six minutes later. By contrast, in FIG. 4, where electric heat remains active for a time after the end of defrost mode, the discharge air temperature rises rather than falls when defrost mode ends. In particular, in this example, the discharge air temperature just after the end of defrost mode rises to approximately 73° F. rather than dropping to approximately 45° F. The discharge air temperature then continues to rise and reaches the approximately 95° F. level within approximately two minutes.

The staging of the deactivation of the electric heat may allow a desired discharge air temperature range to be maintained during defrost recovery. In the example of FIG. 4, the discharge air temperature varies only between approximately 73° F. and approximately 103° F. during defrost recovery. If the stages of electric heat were turned off at different times, different ranges of discharge air temperature may be achieved during defrost recovery.

The example of FIG. 4 depicts discharge air temperatures for an HVAC system with three stages of heating and a total heating capacity of 14.4 kilowatts. In this example, it is desired that the discharge air temperature vary in a range either side of approximately 90° F. during defrost mode and defrost recovery. In other embodiments, these parameters may take other values. The examples of FIGS. 5-9 plot discharge air temperatures for various other values of the number of heating stages, the heating capacity, and the desired discharge air temperature. In all cases, it can be seen that staged activation of electric heat near the beginning of defrost mode and staged deactivation of electric heat during defrost recovery may prevent excessively warm air from being supplied near the beginning of defrost mode and may prevent excessively cool air from being supplied when defrost mode ends.

The examples of FIGS. 4-7 depict what may be referred to as a high comfort method of operating electric heat during defrost mode and defrost recovery. In the high comfort method, the temperature about which the discharge air temperature varies during defrost mode and defrost recovery may be set to a relatively high level. More specifically, the set point 410 in FIG. 4 is 90° F., the set point 510 in FIG. 5 is 85° F., the set point 610 in FIG. 6 is approximately 97° F., and the set point 710 in FIG. 7 is 85° F. In other implementations of the high comfort method, other relatively high discharge air temperature set points may be used. Discharge air temperatures at such levels may be deemed comfortable by many comfort zone occupants. However, more energy may be needed for the electric heat to maintain the discharge air temperature at such levels than at lower levels.

The examples of FIGS. 8 and 9 depict what may be referred to as a net capacity method of operating electric heat during defrost mode and defrost recovery. In the net capacity method, the temperature about which the discharge air temperature varies during defrost mode and defrost recovery may be set to a relatively low level. More specifically, the set point 810 in FIG. 8 is 70° F., and the set point 910 in FIG. 9 is 65° F. In other implementations of the net capacity method, other relatively low discharge air temperature set points may be used. The net capacity method may save energy compared to the high comfort method, but discharge air temperatures at such levels may feel less comfortable to some comfort zone occupants than the levels maintained in the high comfort method.

In an embodiment, an HVAC system may provide a plurality of options related to staging electric heat during defrost mode and defrost recovery. Each of the options may offer a different tradeoff between energy savings and comfort by offering a different combination of the number of heating stages, the heating capacities of the stages, the timing of the activation and deactivation of the stages, the desired discharge air temperature during defrost mode and defrost recovery, and other parameters. In some embodiments, only two operating methods, such as the high comfort method and the net capacity method, are provided. In other embodiments, two or more operating methods may be provided that are similar to the high comfort method and the net capacity method but have different levels of tradeoff between energy savings and comfort. In other embodiments, the traditional method of using electric heat without staging, as depicted in FIG. 3, may be provided as another option in addition to the methods that use staging. This option may be referred to as the normal operation method. In other embodiments, the use of no electric heat at all, as depicted in FIG. 2, may be provided as another option in addition to the methods that use electric heat. This option may be referred to as the high efficiency method. The latter option may be the most energy efficient but may offer the least comfort and so is likely to be selected only when the greatest possible energy savings are desired.

In an embodiment, an HVAC system may provide users of the system with an opportunity to choose a desired operating method for electric heat. For example, the HVAC system may offer a choice between the high comfort method and the net capacity method; between the high comfort method, the net capacity method, and the normal operation method; between the high comfort method, the net capacity method, the normal operation method, and the high efficiency method; between two or more operating methods similar to the high comfort method and the net capacity method but with different levels of tradeoff between energy savings and comfort; or between some other combination of operating methods.

The choice may be provided as an option on a thermostat, a comfort control, or some other type of control mechanism, such as the communicating thermostat 130 of FIG. 1. In some cases, the choice may be displayed as a plurality of named options such as “high comfort”, “high efficiency”, or the like. A user may press a button on the control mechanism, select a menu item on the control mechanism, select an icon on the control mechanism, or perform some other action to select one of the options. In other cases, the choice may be displayed as a scale, where it is understood that options at one end of the scale offer more comfort and options at the other end of the scale offer greater energy savings. A user may select a setting at a point along the scale. In other cases, the choice may be displayed and selected in other ways.

Examples of procedures that may be followed in activating electric heat in stages in defrost mode and deactivating electric heat in stages in defrost recovery are provided below for the high comfort and net capacity methods. It should be understood that these are only examples and that other procedures and other values for variables could be used.

T_(DD)=Demand Discharge Temperature for defrost and defrost recovery

T_(SA)=Supply Air Temperature (measured) between indoor coil and electric heat

T_(DA)=Discharge Air Temperature (calculated) after electric heat

ΔT_(EH)=Temperature rise across the electric heater at given airflow

ΔH_(ADJ)=Heat rise adjustment factor for electric heater coils

ΔD_(EH)=% Demand adjustment for Electric Heat

L=15 seconds (interval between updates to discharge temperature)

NOTE: ΔH_(ADJ) is 1.08 for Nikrothal® N60 wire planned for electric heater elements; 3412.142 is factor for conversion from BTU/hr to kW.

${\Delta \; T_{EH}} = \left( \frac{{EH}\mspace{14mu} {Actual}\mspace{14mu} {Capacity}}{\left( {\Delta \; {H_{ADJ}/3412.142}} \right)*{Actual}\mspace{14mu} {Airflow}} \right)$ T_(DA) = T_(SA) + Δ T_(EH)

Defrost

% Demand=MIN{% Demand+ΔD _(EH), INT(CC demand stages/CC configured stages)*100%)}

Defrost Recovery

% Demand=MAX{% Demand−ΔD _(EH), 0%}

NOTE: % Demand≦INT(CC demand stages/CC configured stages)*100%)

Defrost (Maintain T_(DD)±5° F.)

% Demand=0

ΔD_(EH)=10%

Initial EH demand starts at 0; will add EH capacity to maintain discharge air temperature while Defrost state=TRUE

if L ≧ 15 seconds then Get T_(SA) T_(DA) = T_(SA) + ΔT_(EH) if % Demand ≦(CC demand stages / CC configured stages) * 100% AND T_(DA) < T_(DD) − 5°F then % Demand = % Demand + ΔD_(EH) Increment % Demand by 10% every 15 seconds during defrost while calculated discharge temperature is < T_(DD) − 5°F endif endif endwhile return Defrost

Defrost Recovery (Maintain T_(DD)±5° F.)

Previous state was Defrost; if Heat/Cool Demand changes, exit recovery while Defrost Recovery state=TRUE

if L ≧ 15 seconds then Get T_(SA) T_(DA) = T_(SA) + ΔT_(EH) if % Demand ≦(CC demand stages / CC configured stages) * 100% AND T_(DA) ≧ T_(DD) + 5°F then % Demand = % Demand − ΔD_(EH) Decrement % Demand by 10% every 15 seconds during defrost while calculated discharge temperature is ≧ T_(DD) + 5°F endif endif endwhile return Defrost

It can be seen that measurements and calculations are made to determine a percentage related to the amount of electric heat that needs to be provided to achieve a desired discharge air temperature. This percentage of electric heat demand may be related to the number of stages of electric heat to be activated. For example, if two stages of electric heat are available and the demand for electric heat is less than 50%, only one stage of electric heat may be activated. If the demand for electric heat is 50% or more, both stages of electric heat may be activated. If three stages of electric heat are available and the demand for electric heat is less than 33%, only one stage of electric heat may be activated. If the demand for electric heat is 33% to 66%, two stages of electric heat may be activated. If the demand for electric heat is greater than 66%, all three stages of electric heat may be activated. In other examples, the percentage of electric heat demand may be related in other ways to the number of stages of electric heat that are activated. Similar concepts may apply to greater numbers of stages.

FIG. 10 is a flow chart illustrating an embodiment of a method 1000 for operating an HVAC system such as HVAC system 100. At block 1010, when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, a supplemental heat generator that was in operation in the defrost mode continues to operate. At block 1020, after a period of time in the defrost recovery mode has passed, at least a first portion or stage of the total heating capacity of the supplemental heat generator is deactivated. If the supplemental heat generator has a plurality of portions or stages of total heating capacity, then at block 1030, after an additional period of time in the defrost recovery mode has passed, at least one additional portion or stage of the total heating capacity of the supplemental heat generator is deactivated. The deactivations of the portions or stages may continue until the total heating capacity of the supplemental heat generator is deactivated.

The HVAC system 100 described above may comprise a processing component (such as controller processor 132 and/or the thermostat processor 136 shown in FIG. 1) that is capable of executing instructions related to the actions described previously. The controller processor 132 and/or the thermostat processor 136 may be a component of a computer system. FIG. 11 illustrates a typical, general-purpose computer system 1300 that includes a processing component 1310 suitable for implementing one or more embodiments disclosed herein. In addition to the processor 1310 (which may be referred to as a central processor unit or CPU), the system 1300 might include network connectivity devices 1320, random access memory (RAM) 1330, read only memory (ROM) 1340, secondary storage 1350, and input/output (I/O) devices 1360. In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processor 1310 might be taken by the processor 1310 alone or by the processor 1310 in conjunction with one or more components shown or not shown in the drawing.

The processor 1310 executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices 1320, RAM 1330, ROM 1340, or secondary storage 1350 (which might include various disk-based systems such as hard disk, floppy disk, or optical disk). While only one processor 1310 is shown, multiple processors may be present. Thus, while instructions may be discussed as being executed by a processor, the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors. The processor 1310 may be implemented as one or more CPU chips.

The network connectivity devices 1320 may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices 1320 may enable the processor 1310 to communicate with the Internet or one or more telecommunications networks or other networks from which the processor 1310 might receive information or to which the processor 1310 might output information.

The network connectivity devices 1320 might also include one or more transceiver components 1325 capable of transmitting and/or receiving data wirelessly in the form of electromagnetic waves, such as radio frequency signals or microwave frequency signals. Alternatively, the data may propagate in or on the surface of electrical conductors, in coaxial cables, in waveguides, in optical media such as optical fiber, or in other media. The transceiver component 1325 might include separate receiving and transmitting units or a single transceiver. Information transmitted or received by the transceiver 1325 may include data that has been processed by the processor 1310 or instructions that are to be executed by processor 1310. Such information may be received from and outputted to a network in the form, for example, of a computer data baseband signal or signal embodied in a carrier wave. The data may be ordered according to different sequences as may be desirable for either processing or generating the data or transmitting or receiving the data. The baseband signal, the signal embedded in the carrier wave, or other types of signals currently used or hereafter developed may be referred to as the transmission medium and may be generated according to several methods well known to one skilled in the art.

The RAM 1330 might be used to store volatile data and perhaps to store instructions that are executed by the processor 1310. The ROM 1340 is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage 1350. ROM 1340 might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM 1330 and ROM 1340 is typically faster than to secondary storage 1350. The secondary storage 1350 is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM 1330 is not large enough to hold all working data. Secondary storage 1350 may be used to store programs that are loaded into RAM 1330 when such programs are selected for execution.

The I/O devices 1360 may include liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, or other well-known input or output devices. Also, the transceiver 1325 might be considered to be a component of the I/O devices 1360 instead of or in addition to being a component of the network connectivity devices 1320.

At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R_(l), and an upper limit, R_(u), is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. 

What is claimed:
 1. A method of operating an HVAC system, comprising: when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, continuing to operate a supplemental heat generator that was in operation in the defrost mode; and after a period of time in the defrost recovery mode has passed, deactivating at least a first portion of the total heating capacity of the supplemental heat generator.
 2. The method of claim 1, further comprising, when the supplemental heat generator has a plurality of portions of total heating capacity, after an additional period of time in the defrost recovery mode has passed, deactivating at least one additional portion of the total heating capacity of the supplemental heat generator, the deactivations of the portions continuing until the total heating capacity of the supplemental heat generator is deactivated.
 3. The method of claim 1, wherein the HVAC system provides a plurality of options for operation of the supplemental heat generator, the plurality of options including: at least a first option that provides relatively warmer discharge air in the defrost mode and the defrost recovery mode and uses a relatively greater amount of energy; and at least a second option that provides relatively cooler discharge air in the defrost mode and the defrost recovery mode and uses a relatively smaller amount of energy, wherein the discharge air temperature and the energy usage are at least partially controlled by activation and deactivation of the supplemental heat generator.
 4. The method of claim 3, wherein the plurality of options for operation of the supplemental heat generator further includes an option wherein operation of the supplemental heat generator ceases when the defrost mode ends.
 5. The method of claim 4, wherein the plurality of options for operation of the supplemental heat generator further includes an option wherein the supplemental heat generator is not operated.
 6. The method of claim 3, wherein the HVAC system includes a control mechanism that displays the plurality of options for operation of the supplemental heat generator and allows one of the plurality of options to be selected.
 7. The method of claim 1, wherein, when the supplemental heat generator is activated in the defrost mode, less than the total heating capacity of the supplemental heat generator is activated, and wherein at least one additional portion of the total heating capacity of the supplemental heat generator is activated at a later time, the activations of the portions continuing until the total heating capacity of the supplemental heat generator is activated or until a desired discharge air temperature is reached.
 8. An HVAC system, comprising: a supplemental heat generator configured such that, when a defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, the supplemental heat generator continues operation that began in the defrost mode, and further configured such that, after a period of time in the defrost recovery mode has passed, at least a first portion of the total heating capacity of the supplemental heat generator is deactivated.
 9. The HVAC system of claim 8, wherein the supplemental heat generator is further configured such that, when the supplemental heat generator has a plurality of portions of total heating capacity, after an additional period of time in the defrost recovery mode has passed, at least one additional portion of the total heating capacity of the supplemental heat generator is deactivated, the deactivations of the portions continuing until the total heating capacity of the supplemental heat generator is deactivated.
 10. The HVAC system of claim 8, wherein the HVAC system provides a plurality of options for operation of the supplemental heat generator, the plurality of options including: at least a first option that provides relatively warmer discharge air in the defrost mode and the defrost recovery mode and uses a relatively greater amount of energy; and at least a second option that provides relatively cooler discharge air in the defrost mode and the defrost recovery mode and uses a relatively smaller amount of energy, wherein the discharge air temperature and the energy usage are at least partially controlled by activation and deactivation of the supplemental heat generator.
 11. The HVAC system of claim 10, wherein the plurality of options for operation of the supplemental heat generator further includes an option wherein operation of the supplemental heat generator ceases when the defrost mode ends.
 12. The HVAC system of claim 11, wherein the plurality of options for operation of the supplemental heat generator further includes an option wherein the supplemental heat generator is not operated.
 13. The HVAC system of claim 10, wherein the HVAC system includes a control mechanism that displays the plurality of options for operation of the supplemental heat generator and allows one of the plurality of options to be selected.
 14. The HVAC system of claim 8, wherein, when the supplemental heat generator is activated in the defrost mode, less than the total heating capacity of the supplemental heat generator is activated, and wherein at least one additional portion of the total heating capacity of the supplemental heat generator is activated at a later time, the activations of the portions continuing until the total heating capacity of the supplemental heat generator is activated or until a desired discharge air temperature is reached.
 15. A method of operating an HVAC system, comprising: when a supplemental heat generator in the HVAC system is activated in a defrost mode of the HVAC system, activating less than the total heating capacity of the supplemental heat generator; and when the defrost mode of the HVAC system ends and a defrost recovery mode of the HVAC system begins, continuing to operate the supplemental heat generator.
 16. The method of claim 15, wherein at least one additional portion of the total heating capacity of the supplemental heat generator is activated at a later time in the defrost mode, the activations of the portions continuing until the total heating capacity of the supplemental heat generator is activated or until a desired discharge air temperature is reached.
 17. The method of claim 15, wherein, after a period of time in the defrost recovery mode has passed, a first portion of the total heating capacity of the supplemental heat generator is deactivated, and wherein, after an additional period of time in the defrost recovery mode has passed, at least one additional portion of the total heating capacity of the supplemental heat generator is deactivated, the deactivations of the portions continuing until the total heating capacity of the supplemental heat generator is deactivated.
 18. The method of claim 15, wherein the HVAC system provides a plurality of options for operation of the supplemental heat generator, the plurality of options including: at least a first option that provides relatively warmer discharge air in the defrost mode and the defrost recovery mode and uses a relatively greater amount of energy; and at least a second option that provides relatively cooler discharge air in the defrost mode and the defrost recovery mode and uses a relatively smaller amount of energy, wherein the discharge air temperature and the energy usage are at least partially controlled by activation and deactivation of the supplemental heat generator.
 19. The method of claim 18, wherein the plurality of options for operation of the supplemental heat generator further includes an option wherein operation of the supplemental heat generator ceases when the defrost mode ends and an option wherein the supplemental heat generator is not operated.
 20. The method of claim 18, wherein the HVAC system includes a control mechanism that displays the plurality of options for operation of the supplemental heat generator and allows one of the plurality of options to be selected. 